Transportation systems and networks do not exist in and of themselves. They represent a crucial service-often public but increasingly private-that provides mobility. Moreover, like all services that provide fundamental economic and social value, they must increase the value they provide to society. Too often, policy recommendations adopting a sustainability label implicitly accept a static policy making environment and focus on redistributing existing resources rather than thinking about how the stock of resources might be improved. This may be even more important in transportation than in other parts of the economy and society. Increased mobility, in fact, leads to greater economic productivity, allowing us to use existing resources more effectively and efficiently. Moreover, technology and innovation can easily make what now seems like a very scarce and limited resource obsolete within a generation. Oil is probably the best contemporary example of this phenomenon. As the BRIC-Brazil, Russia, India, and China-economies grow at astounding rates, the demand for oil is likely to outstrip supply for a while, pushing prices up. Moreover, many energy analysts believe we have already met “peak oil”-that point where we no longer discover new reserves at a pace sufficient to keep up with current consumption. This geological reality has prompted many in the policymaking community to naively rush into heavily subsidizing alternative fuels such as ethanol since these rates of growth in the demand for oil are unsustainable. Many nations and cities have also started to embrace more draconian ideas such as cordon charges and other fees to explicitly limit customized travel options such as the use of automobiles. This is unfortunate, because strategies that focus on reducing automobile use are not sustainable in an economic or an environmental sense. From an economic perspective, efforts to push travelers and commuters into public transit inevitably have one of two effects. First, it lengthens commute and travel times, reducing productivity and compromising the ability of our cities compete to globally. Our cities benefit from faster travel times, not slower ones. Moreover, faster travel times count for human resources, not just transporting capital goods. Second, strategies that explicitly attempt to limit automobile based travel force people (and businesses) into higher densities. While higher densities (and more mixed uses) are not necessarily negative, the trade offs often include a much higher cost of living and lower mobility. The key policy issue is whether these choices are made voluntarily-a demand side response that should enhance social welfare-or are forced through supply side limits-a response that compromises welfare by forcing citizens and businesses to accept a “second best” outcome. The economies that focus on “first best” outcomes are the ones that will survive and prosper. In short, public policy focused on maximizing transportation performance will compete and be sustainable.